Recently, lithium secondary batteries have become the subject of profound interest as they represent the newest generation of high-performance secondary batteries. The advantages of lithium secondary batteries include their high energy density, steady discharging characteristic, wide range of working temperatures, long shelf life, good safety, and low environmental pollution, etc. Lithium secondary batteries can be widely used in mobile phones, notebook personal computers, personal digital assistants, cameras, camcorders, portable VCRs, etc. The market potential and the economic significance of the lithium secondary batteries cannot be overstated.
At present, the cathode materials used in lithium batteries mainly belong to one of the three types: LiCoO.sub.2, LiNiO.sub.2, and LiMn.sub.2 O.sub.4. All of these cathode materials can provide voltages over 3 volts, with LiCoO.sub.2 providing the highest voltage--as high as 4 volts. The higher the voltage provided by a battery cell, obviously, the lower the number of battery cells that will be required to form a battery unit of desired overall voltage. Since the energy density provided by a battery cell is the product of battery voltage and its capacity, a battery cell with higher voltage output also provides higher energy density. Therefore, in the search for high energy density battery cells, it is important to develop cathode materials that will generate high voltage.
In 1961, J. C. Bemier, et al., discovered that the crystal structures of LiNiVO.sub.4 and LiCoVO.sub.4 belonged to that of an inverse spinel. They used the following procedure to synthesize these materials: ##STR1## The above method is not very practical in that it requires very long synthesis time, seven days, thus it does not meet the commercially acceptable economic criteria.
In 1979, Y. Ito published an article, in which it was disclosed that LiNiVO.sub.4 can be synthesized in 100 hours at 1,000.degree. C., with a system of reactants, LiVO.sub.3 and NiO, at a molar ratio of 1:1. Although the method disclosed by Ito substantially reduced the synthesis time for LiNiVO.sub.4 from 7 days to 4 days, it requires that the reaction be conducted at a very high temperature of 1,000.degree. C.; this makes the process economically unattractive. Also the reaction time of 4 four days does not meet the economic criteria. Prior to the synthesis process, it was necessary to first synthesize the reactants by mixing and reacting NiO.sub.4, V.sub.2 O.sub.5, and Li.sub.2 O, in appropriate proportions. This also adds to the production cost. Furthermore, it was discovered that, with this high-temperature process, the lithium atoms were wedged inside the metallic oxide structure. Also, at temperatures above 850.degree. C., some "fusion" occurred during the reaction, and the reactants reacted with the reactor material.